The O.M. specifically warns against using anything but 5W-20 oil for the Hemi, because of the MDS system that uses engine oil pressure to activate linkages in the valve train to de-activate 4 cylinders. Sounds like something that could be a very expensive experiment if it goes wrong.
They changed recommendations over the years in the O.M., so definitely check your MY O.M., because it may be different.
An SRT8 probably is equipped with the 6.1L HEMI, which did NOT have MDS, so using a different viscosity oil probably is NOT as bad as a 5.7L HEMI with MDS.
What happens with MDS if you use a different viscosity, I don't know, and I would NOT be surprised at all if you can't notice a difference. BUT, considering the stress the valve train is under and the MDS system only increases that stress, I also would NOT be surprised if using the wrong viscosity oil could create a different response in the system that results in excessive wear or increased chance of breakage.
So, I have to ask, the engineers that designed and spent thousands of hours testing the HEMI came up with a recommendation of what the best oil viscosity is to use, what have you come up with as the reason to use the viscosity that you use?
NOT that I'm that against doing something different than the manufacturers recommendation, if you have a good reason or good evidence to do otherwise, BUT, so often when I see people using an oil viscosity far different than recommended, there reason is nonsense, e.g. "I heard good things about this oil", "It's what I used in my other car and it worked well", "Ferraris use this viscosity oil", etc...
Yes, good quality Synthetic (there are a lot of pretenders that aren't as good out there) you can go to different viscosities and protect as well as the recommended viscosity. Yes, there are Racing Teams that make the conscience decision to use lighter viscosity oils for the gains in less pumping losses and rebuild the engine every season, so there are good reasons, as long as people know what they are getting into and actually measure the differences and figure out if they made a good decision or NOT.
What does your oil pressure gauge show for difference in oil pressures for different conditions when using the 0W-40 viscosity?
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